Undetected and unimpeded submarine communication with surface or above surface vehicles is a highly desired objective. Present methods require submarine performance which interfere with best operational depth and/or speed. Several of the present methods also entail a high degree of possible detection by unwanted sources.
Some types of electromagnetic radiation systems have been utilized from below the surface. However, these systems such as a trailing-wire or loop do not permit high power or low frequency signals, nor are they reliable due to their low power output. They also constrain the depth and speed of the submarine operation when communication is taking place.
Another system is to place an electromagnetic radiating element on the surface (connected of course to the submarine). This has several disadvantages, among them restriction on submarine speed and/or depth, the element takes several minutes to reach the surface; and the element can be detected on the surface giving away the submarine location.
Still a further system involves the use of laser, dye or smoke emission. These of course only work under good visibility and sea conditions and are of course visible to all-friend or foe, and of course beside the other constraints this method is not very effective in communicating with other submarines or to surface ships.
A low frequency communication system would present a significant advance over the above systems and is particularly desired because of the penetration through a medium (water) of the low frequency electromagnetic waves. However, low frequency communication has always been difficult because of the physical size requirements of the antenna structure. A successful method known to the prior art of generating low frequency waves (below 1000 Hz) has been the SANGUINE Project, which essentially employs the earth as a radiator. Simply stated, a grounded transmission line is placed over a huge rock deposit. Since the rock deposit usually has a relatively low conductivity, the transmission line forms an effective loop antenna many kilometers deep. Obviously, this loop is immmoveable and not of practical use on a submarine, but it shows the magnitude of the problem involved.